Why Does the Holy Month of Ramadan Start and End at Different Dates Every Year?

Why does the holy month of Ramadan come 10 days earlier each year?

Answer:

In the Quran and hadiths, Islamic commands are proclaimed to the Muslims considering the lunar calendar. The time of Hajj, the starting time of fast, one of the Muslims’ essential worships, the special nights (like laylat-ul Qadr) are all determined based on the lunar calendar.

The period of time that the earth makes one complete revolution around the sun is called the solar year. The length of a solar year that “the Gregorian calendar” is based on is approximately 365 days and 6 hours. (365 days, 5 hours, 48 minutes, 45.51 seconds)

The year consisting of 12 lunar months and based on cycles of the lunar phase is called the lunar year. The calendar based on lunar year is called the “Islamic calendar” or “Hijri-Qamari calendar”.

Moon completes its revolution around the earth in 29, 5 days. This period is called “a month”. One lunar year consists of 12 lunar months which is equal to 12 x 29, 5 = 354 days. It means that lunar year is approximately 11 days less than the solar year. So a lunar month drifts each solar year by 11 days and comes back to the same date in relation to the solar year approximately every 33 Islamic years.